The gauntlet was first thrown inPredator 2. A glimpse inside the visiting spaceship of a band of extraterrestrial hunters revealed a distinctive, elongated skull on the trophy wall. It meant that these Predators, for lack of a better word, had bagged one of the aliens from Aliens. It was the silent shot heard round the sci-fi world. Comics and a pair of aggressively forgettable movies followed, playing out just how these unnamed Predators might face off against the similarly unnamed aliens. Next to the acid-spurting, wall-scrambling aliens, the Predators suddenly seemed almost honorable. They were the lesser evil by far, only dabbling in the occasional murder, while never plotting outright genocide by way of face-hugging reproduction. And with their superhuman physiques, their high-tech arsenal, and giant helmets that usually covered their hideous, mandibled faces, the Predators became bloodthirsty antiheroes.

The new movie Predators, in theaters this week, brings the Predators back to their villainous roots, as they prey on a group of humans dumped into the jungles of the hunters' own home world. They are, it seems, the most perfect killers in all of pop culture, and will go about the bloody work of proving it once again. But if the Predators were real—actual alien life-forms—they would be a species in decline. Here's why.

Predators Are Not Predators

Despite their implied name, the Predators are not really predators at all. According to Stuart Sumida, a professor of biology at California State University-San Bernardino who has worked as a consultant on Hollywood films, successful predators have certain universal traits, and one or two optional ones. Predators need depth perception, preferably from a pair of forward-facing eyeballs. "Anything that's going to catch prey must know where it is in three-dimensional space," Sumida says.

Next is explosive speed, the better to chase down those precisely targeted meals. Finally, a predator needs something sharp, whether it's a beak, claws or teeth. Think of a predator as a kind of guided missile, with the stereoscopic eyes serving as sensors, and, in the case of ground-based animals, a flurry of legs providing thrust. If it connects with the target, the natural weapons kill or disable the prey. Beyond those requirements, everything else is a bonus, such as having keen vision or senses in general.

The Predators have the eyes and the relatively sharp claws (their mandibles are too flimsy to be used in a real fight), but they have the same sluggish bipedal posture as humans. For land predators, a four-legged gait generally provides the necessary speed. Even a no-legged slither is quicker, relative to the animal's size, than a human's run. "It turns out that our posture and locomotion are very efficient. We don't move quickly, but we use very little energy," Sumida says. "We're very good at traveling and moving around the planet."

Like humans, the Predators make up for their lack of speed either by simply conquering distance—making the long-distance hikes necessary to found a civilization—or by using ranged weapons such as spears and, more impressively, shoulder-mounted ray guns (called plasma casters). While a cheetah will outrun a human (or Predator, for that matter) any day, slow and steady wins the race to the top of the food chain. "We think of ourselves as excellent predators. We can kill the planet, it's true, but we've done so because we are toolmakers," Sumida says. The Predators' most unnerving tool has always been their invisibility fields. In the new film, the aliens' new tricks are relatively old ones, such as trained hunting dogs and unmanned aerial vehicles. But the presence of these gadgets and techniques, the ones that make them such effective hunters, poses a larger question:

Why is such an insanely successful species so eager to die?

Suicide of a Species

There are clear parallels between the Predators and present-day humans. Both have mastered their own worlds, thanks to bipedal efficiency and a flair for adaptation. This innovation applies to violence, too. "The Predators title doesn't only refer to the mandibled ones," says the film's director, Nimrod Antal. "It refers to what they're hunting as well. These things come up with all kinds of disturbing ways to kill, which are just as disturbing as what humans do."

The darkness of the human heart aside, what the Predators seem compelled to do with their faster-than-light spacecraft and other impossibly advanced technology is to engage not only in gruesome sport, but to place themselves in grave danger. "To have the technology to go into space like that, with those hunting gadgets, means the Predators would be at a place in society where there aren't any real pressures for survival," said E. Paul Zehr, a professor of neuroscience and kinesiology at the University of Victoria in Canada, and author of Becoming Batman: The Possibility of a Superhero.

Humans seem to be at a similarly stable place, as a species. But apart from the occasional volley of friendly fire, deer hunters don't have much to fear from their pastime, much less from their actual prey. To wade into close-quarters combat with an enraged stag, armed only with a knife and some night-vision goggles, might be the closest equivalent to the Predator experience. This is not a popular human endeavor because it directly contradicts our survival instincts. "Risking their lives like this, it goes beyond dabbling like a dilettante. The Predators have to be deliberately acting against Darwinian pressures," Zehr says. Those pressures should be familiar—less work, more play, and certainly less risk of losing life and limb than one's primitive ancestors risked. In fact, over the centuries and more needed to master time, space and plasma casters, Zehr assumes that the Predators would have evolved to be less physically impressive and more reliant on their tech. If the Predators have not only reinserted the dangers that civilization is supposed to root out, but maintained a constant state of strife, then they've been failing as a species for a long time.

There is at least one example in nature of animals fighting not for food or self-defense, but for a kind of social survival. Male lions occasionally break all the rules of predation, openly charging a group of animals and attacking the biggest of the bunch. This, Zehr says, is about maintaining the alpha position. If the pride's leader goes too long without proving his ability to get into, and live through, a pointless fight, he could lose control and lose his pick of mates. This is an intersection of social and natural selection. Maybe that's why the Predators are willing to cast aside the benefits of evolution and technology, and die at the hands of lower life-forms. Perhaps somewhere out there, there are lady Predators who need impressing.

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